ZnS bubble clusters with onion-like structures

Following recent studies which showed that the most stable structures for (ZnS)(n) clusters (n= 10-47) are the so-called "bubble clusters", in which all the atoms are three-coordinated, we have used simulated annealing techniques to find the most stable structure for a larger cluster, (ZnS)(60). We find an onion-like structure, with one small cluster enclosed inside a bigger one. The inner cluster has the structure of a sodalite cage. Bonding between the inner and the outer clusters creates a network of four-coordinated atoms.     

计算机模拟原子簇的稳定构型和能量性质

用密度泛函(DFT)方法研究了铜原子簇Cu~n(n=2,3,4,6)的稳定几何构型和电子结构。通过拟合从头算势能面构造铜原子簇势能函数的双体、三体及四体项,并利用该函数和全局优化“Basin-Hopping”算法得到较大铜原子簇(n=13～56)能量极小的结构,计算结果与实验及其它计算结果相一致。     

Stochastic search of the quantum conformational space of small lithium and bimetallic lithium-sodium clusters

In this paper we report the results obtained by an implementation and application of the simulated annealing optimization procedure to the exploration of the conformational space of small neutral and charged lithium clusters (Li(n)(q), n = 5, 6, 7; q = 0, +/-1) and of the bimetallic lithium/sodium clusters (Li5Na) in their lowest spin states. Our methodology eliminates the structure guessing procedure in the process of generating cluster configurations. We evaluate the quantum energy, typically with the Hartree-Fock Hamiltonian, of randomly generated points in the conformational space and use a modified Metropolis test in the annealing algorithm to generate candidate structures for atomic clusters. The structures are further optimized by analytical methods (gradient following) at the M?ller-Plesset second order perturbation theory level (MP2), in conjunction with basis sets including polarization functions with and without diffuse functions. High accuracy ab initio energies at the coupled clusters level, with single, double, and triple substitutions from the Hartree-Fock determinant (CCSD(T)), on the MP2 geometries were calculated and used to establish the relative stability of the isomers within each potential energy surface. Various cluster properties were computed and compared to existing values in order to validate our methods. Our results show excellent agreement with previous experimental and theoretical reports. Even at these small sizes, evidence for 10 new structures never reported before for the lithium clusters and four new structures for the bimetallic clusters is presented.     

Size- and shape-dependent polarizabilities of sandwich and rice-ball Co(n)Bz(m) clusters from density functional theory

The dipole polarizabilities of Co(n)Bz(m), (n, m = 1-4, m = n, n + 1) clusters are studied by means of an all-electron gradient-corrected density functional theory and finite field method. The dipole moments are relatively large for most of the clusters, implying their asymmetric structures. The total polarizability increases rapidly as cluster size, whereas the average polarizability shows "odd-even" oscillation with relatively large values at (n, n + 1). The polarizabilities exhibit clear shape-dependent variation, and the sandwich structures have systematically larger polarizability and anisotropy than the rice-ball isomers. The dipole polarizabilities are further analyzed in terms of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap, ionization potential, and electron delocalization volume. We conclude that the polarizability variations are determined by the interplay between the geometrical and electronic properties of the clusters.     

A Gaussian-3 theoretical study of small silicon-lithium clusters: electronic structures and electron affinities of SinLi(-) (n = 2-8)

The molecular structures of neutral Si n Li ( n = 2-8) species and their anions have been studied by means of the higher level of the Gaussian-3 (G3) techniques. The lowest energy structures of these clusters have been reported. The ground-state structures of neutral clusters are "attaching structures", in which the Li atom is bound to Si n clusters. The ground-state geometries of anions, however, are "substitutional structures", which is derived from Si n+1 by replacing a Si atom with a Li (-). The electron affinities of Si n Li and Si n have been presented. The theoretical electron affinities of Si n are in good agreement with the experiment data. The reliable electron affinities of Si n Li are predicted to be 1.87 eV for Si 2Li, 2.06 eV for Si 3Li, 2.01 eV for Si 4Li, 2.61 eV for Si 5Li, 2.36 eV for Si 6Li, 2.21 eV for Si 7Li, and 3.18 eV for Si 8Li. The dissociation energies of Li atom from the lowest energy structures of Si n Li and Si atom from Si n clusters have also been estimated respectively to examine relative stabilities.     

包含两个平面五配位碳原子C_(2+n)B_(10-n)(n=0～10)团簇的结构的理论研究

采用B3LYP/6-311+G**方法,我们优化了初始构型中包含两个平面五配位碳原子(ppCs)的C2+nB10-n(n=0～10)团簇的结构并计算了它们的振动频率.计算结果表明,C2+nB10-n(n=0～2)团簇是稳定的,而且这三个结构中ppC—B键的Wiberg键级介于0.511～0.909之间,ppC—C键的Wiberg键级为0.2254(n=1)和0.8586(n=2),ppC的键级介于3.778到3.879之间,即这三个结构中存在两个ppCs,而且ppC遵循八隅规则;C2+nB10-n(n=3～6)团簇的最稳定结构包含一个ppC;C2+nB10-n(n6)团簇能量最低结构中不存在ppC.而且只有团簇C2+nB10-n(n=0～2)中没有悬键,它们的π电子数分别为:6,7和8,计算它们的NICS(0)值表明强芳香性一般位于局部的三元环中心,表明局部离域有利于平面结构的形成.C2+nB10-n(n=0～2)团簇的第一垂直激发能分别为:1.91,0.56和3.12eV.     

Quantum Chemical Study of CnAl2^± （n=1～10） Clusters： Structure and Stability

Geometries, electronic structures and vibrational frequencies of CnAl2± clusters have been investigated by using the B3LYP-DFT method in the range of n = 1～10. At the B3LYP/6-311G level, the ground state structures of CnAl2± clusters are planar or linear with terminal aluminum atom. In these structures, the C–C bonds are alternately changed between double and triple. The changing magnitude of the averaged bond length decreases with the increase of cluster size. The energetic analysis showed that CnAl2± clusters with even n are more stable than those with odd n.     

Structural and energetic properties of Ni-Cu bimetallic clusters

The lowest-energy structures for all compositions of Ni n Cu m bimetallic clusters with N = n + m up to 20 atoms, N = 23, and N = 38 atoms have been determined using a genetic algorithm for unbiased structure optimization in combination with an embedded-atom method for the calculation of the total energy for a given structure. Comparing bimetallic clusters with homoatomic clusters of the same size, it is shown that the most stable structures for each cluster size are composed entirely of Ni atoms. Among the bimetallic clusters in the size range N = 2-20, the Ni N-1 Cu 1 clusters possess the highest stability. Further, it has been established that most of the bimetallic cluster structures have geometries similar to those of pure Ni clusters. The size N = 38 presents a special case, as the bimetallic clusters undergo a dramatic structural change with increasing atom fraction of Cu. Moreover, we have identified an icosahedron, a double, and a triple icosahedron with one, two, and three Ni atoms at the centers, respectively, as particularly stable structures. We show that in all global-minimum structures Ni atoms tend to occupy mainly high-coordination inner sites, and we confirm the segregation of Cu on the surface of Ni-Cu bimetallic clusters predicted in previous studies. Finally, it is observed that, in contrast to the bulk, the ground-state structures of the 15-, 16-, and 17-atom bimetallic clusters do not experience a smooth transition between the structures of the pure copper and the pure nickel clusters as a function of the relative number of the two types of atoms. For these sizes, the concentration effect on energy is more important than the geometric one.     

Simulated annealing and density functional theory calculations of structural and energetic properties of the ammonium chloride clusters (NH4Cl)n, (NH4+)(NH4Cl)n, and (Cl-)(NH4Cl)n, n = 1-13

Simulated annealing Monte Carlo conformer searches using the "mag-walking" algorithm are employed to locate the global minima of molecular clusters of ammonium chloride of the types (NH(4)Cl)(n), (NH(4)(+))(NH(4)Cl)(n), and (Cl(-))(NH(4)Cl)(n) with n = 1-13. The M06-2X density functional theory method is used to refine and predict the structures, energies, and thermodynamic properties of the neutral, cation, and anion clusters. For selected small clusters, the resulting structures are compared to those obtained from a variety of models and basis sets, including RI-MP2 and B3LYP calculations. M06-2X calculations predict enhanced stability of the (NH(4)(+))(NH(4)Cl)(n) clusters when n = 3, 6, 8, and 13. This prediction corresponds favorably to anomalies previously observed in thermospray mass spectroscopy experiments. The (NH(4)Cl)(n) clusters show alternations in stability between even and odd values of n. Clusters of the type (Cl(-))(NH(4)Cl)(n) display a magic number distribution different from that of the cation clusters, with enhanced stability predicted for n = 2, 6, and 11. None of the observed cluster structures resemble the room-temperature CsCl structure of NH(4)Cl(s), which is consistent with previous work. Numerous clusters have structures reminiscent of the higher-temperature, rock-salt phase of the solid ammonium halides.     

Structures and relative stability of medium-sized silicon clusters. IV. Motif-based low-lying clusters Si21-Si30

Structures and relative stability of four families of low-lying silicon clusters in the size range of Sin(n=21-30) are studied, wherein two families of the clusters show prolate structures while the third one shows near-spherical structures. The prolate clusters in the first family can be assembled by connecting two small-sized magic clusters Sin (n=6, 7, 9, or 10) via a fused-puckered-hexagonal-ring Si9 unit (a fragment of bulk diamond silicon), while those in the second family can be constructed on the basis of a structural motif consisting of a puckered-hexagonal-ring Si6 unit (also a fragment of bulk diamond silicon) and a small-sized magic cluster Sin (n=6, 7, 9, or 10). For Si21-Si29, the predicted lowest-energy clusters (except Si27) exhibit prolate structures. For clusters larger than Si25, the third family of near-spherical clusters becomes energetically competitive. These near-spherical clusters all exhibit endohedral cagedlike structures, and the cages are mostly homologue to the carbon-fullerene cages which consist of pentagons and hexagons exclusively. In addition, for Si26-Si30, we construct a new (fourth) family of low-lying clusters which have "Y-shaped" three-arm structures, where each arm is a small-sized magic cluster (Si6, Si7, or Si10). Density-functional calculation with the B3LYP functional shows that this new family of clusters is also energetically competitive, compared to the two prolate and one near-spherical low-lying families.     

Structure, bonding, and magnetism in manganese clusters

We investigate the structures and magnetic properties of small Mn(n) clusters in the size range of 2-13 atoms using first-principles density functional theory. We arrive at the lowest energy structures for clusters in this size range by simultaneously optimizing the cluster geometries, total spins, and relative orientations of individual atomic moments. The results for the net magnetic moments for the optimal clusters are in good agreement with experiment. The magnetic behavior of Mn(n) clusters in the size range studied in this work ranges from ferromagnetic ordering (large net cluster moment) for the smallest (n=2, 3, and 4) clusters to a near degeneracy between ferromagnetic and antiferromagnetic solutions in the vicinity of n=5 and 6 to a clear preference for antiferromagnetic (small net cluster moment) ordering at n=7 and beyond. We study the details of this evolution and present a picture in which bonding in these clusters predominantly occurs due to a transfer of electrons from antibonding 4s levels to minority 3d levels.     

若干新型结构和新的成键方式的金属羰基簇合物

本文介绍了几位作者所合成并用X射线单晶结构分析表征的五类新型Fe,Co,Ru羰基簇合物。讨论其成键方式与结构特点。并介绍某些具有双键的配位基以不同的断裂方式提供不同的分子片配位于原子簇骨架的情况。     

Appearance of the bulk motif in Al clusters

We have performed an unbiased search for the lowest-energy structures of medium-sized aluminum clusters Al(n) (n=19-26) using a genetic algorithm (GA) coupled with a tight-binding interatomic potential. Structural candidates obtained from our GA search were further optimized using density functional theory. It is found that the double icosahedron is not the most stable structure for Al(19) but serves as the core for Al(20) and Al(21). The lowest-energy structures of Al(n) are found to undergo a transition to an aluminum bulk motif above Al(23). In particular, the lowest-energy structure of Al(26) is almost a fragment of the bulk face-centered-cubic crystal except for the stacking fault at the bottom layer. Anion clusters were also studied.     

Ab initio study of hydrated sodium halides NaX(H2O)(1-6) (X=F, Cl, Br, and I)

We have studied the dissociation phenomena of sodium halides by water molecules. The structures, binding energies, electronic properties, and IR spectroscopic features have been investigated by using the density-functional theory, second-order Moller-Plesset perturbation theory, and coupled clusters theory with single, double, and perturbative triplet excitations. In the case that the sodium halides are hydrated by three water molecules, the most stable structures show the partial (or half) dissociation feature. The dissociated structures are first found for NaX(H2O)(n=5) for X=BrI, though these structures are slightly higher in energy than the global minimum-energy structure. In the case of hexahydrated sodium halides the global minimum-energy structures (which are different from the structures reported in any previous work) are found to be dissociated (X=F/I) or partially/half dissociated (X=Cl/Br), while other nearly isoenergetic structures are undissociated, and the dissociated cubical structures are higher in energy than the corresponding global minimum-energy structure.     

Isomer selective infrared spectroscopy of neutral metal clusters

We report experimental infrared spectra of neutral metal clusters in the gas phase. Multiple photon dissociation of the argon complexes of niobium clusters is used to obtain vibrational spectra in the 80-400 cm(-1) region. The observed spectra for Nb(9)Ar(n) (n=1-4) are different for different values of n. This is explained by the presence of two isomers of Nb(9) that have different affinities towards Ar and the isomer specific infrared spectra are obtained. The structures of the isomers are determined by comparing the observed spectra with the outcome of density-functional theory calculations.     

Theoretical study of Al(n) and Al(n)O (n = 2-10) clusters

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(n) (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al5(+), Al9(+), Al9(-), Al10, Al10(+), and Al10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al3, Al7, Al7(+), and Al7(-) structures are more stable than their neighbors according to their binding energies. For Al7(+) with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al(n) (n = 2-10) clusters, the Al(n)O (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Al(n-1)OAl motif, of which the Al(n-1) part retains the stable structure of pure aluminum clusters.     

Alkali-ion microsolvation with benzene molecules

The target of this investigation is to characterize by a recently developed methodology, the main features of the first solvation shells of alkaline ions in nonpolar environments due to aromatic rings, which is of crucial relevance to understand the selectivity of several biochemical phenomena. We employ an evolutionary algorithm to obtain putative global minima of clusters formed with alkali-ions (M(+)) solvated with n benzene (Bz) molecules, i.e., M(+)-(Bz)(n). The global intermolecular interaction has been decomposed in Bz-Bz and in M(+)-Bz contributions, using a potential model based on different decompositions of the molecular polarizability of benzene. Specifically, we have studied the microsolvation of Na(+), K(+), and Cs(+) with benzene molecules. Microsolvation clusters up to n = 21 benzene molecules are involved in this work and the achieved global minimum structures are reported and discussed in detail. We observe that the number of benzene molecules allocated in the first solvation shell increases with the size of the cation, showing three molecules for Na(+) and four for both K(+) and Cs(+). The structure of this solvation shell keeps approximately unchanged as more benzene molecules are added to the cluster, which is independent of the ion. Particularly stable structures, so-called "magic numbers", arise for various nuclearities of the three alkali-ions. Strong "magic numbers" appear at n = 2, 3, and 4 for Na(+), K(+), and Cs(+), respectively. In addition, another set of weaker "magic numbers" (three per alkali-ion) are reported for larger nuclearities.     

Structures and relative stability of medium-sized silicon clusters. V. Low-lying endohedral fullerenelike clusters Si31-Si40 and Si45

We have performed unconstrained search for low-lying structures of medium-sized silicon clusters Si(31)-Si(40) and Si(45), by means of the minimum-hopping global optimization method coupled with a density-functional based tight-binding model of silicon. Subsequent geometric optimization by using density-functional theory with the PBE, BLYP, and B3LYP functionals was carried out to determine the relative stability of various candidate low-lying silicon clusters obtained from the unconstrained search. The low-lying characteristics of these clusters can be affirmed by comparing the binding energies per atom of these clusters with previously determined lowest-energy clusters(Si(n)) in the size range of 21相似文献   

(HAINH)_n(n=1～6)簇的结构、红外光谱和热力学性质的研究

用自洽场理论(HF)和密度泛函理论(DET)的B3LYP方法,在6-31G~μ水平上研究了HAINH的低聚物(HAINH)_n(n=1～6)簇的几何构型、电子结构、红外光谱和化学热力学性质,并比较了(HAINH)_n和(CIAINH)_n两种低聚物对应结构中化学键强弱,分析了引起(AIN)_n骨架结构发生变化的原因.结果表明,(HAINH)_n簇的基态结构为C_8(n=1),D_(2h)(n=2),D_(3h)(n=3),T_d(n=4),C_s(n=5)和D_(3d)(n=6)对称点群.HAINH基态结构中,AI-N键是三重键.在D_(2h)(n=2)和D_(3h)(n=3)结构中,所有AI-N键均为二重键.在Td(n=4)和D_(3d)(n=6)中,AI-N键为正常单键,而在C_s(n=5)结构中含有三种AI-N键:单键、双键和混合键.振动频率计算表明,结构a～f均为基态稳定结构.热力学计算给出的稳定性顺序为:f>d>e>c>b>a.     

(HAlNH)~n(n=1～6)簇的结构、红外光谱和热力学性 质的研究

用自洽场理论(HF)和密度泛函理论(DFT)的B3LYP方法,在6-31G水平上研究了HAlNH的低聚物(HAlNH)~n(n=1～6)簇的几何构型、电子结构、红外光谱和化学热力学性质,并比较了(HAlNH)~n和(ClAlNH)~n两种低聚物对应结构中化学键强弱,分析了引起(AlN)~n骨架结构发生变化的原因。结果表明,(HAlNH)~n簇的基态结构为C~s(n=1),D~2~h(n=2),D~3~h(n=3),T~d(n=4),C~s(n=5)和D~3~d(n=6)对称点群。HAlNH基态结构中,Al-N键是三重键。在D~2~h(n=2)和D~3~h(n=3)结构中,所有Al-N键均为二重键。在T~d(n=4)和D~3~d(n=6)中,Al-N键为正常单键,而在C~s(n=5)结构中含有三种Al-N键：单键、双键和混合键。振动频率计算表明,结构a～f均为基态稳定结构。热力学计算给出的稳定性顺序为：f>d>e>c>b>a。